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Transcript
Key Ideas • What determines the direction in which passive transport occurs? • Why is osmosis important? • How do substances move against their concentration gradients? 8-2 Cell Transport Cell Transport • Must move substances of varying size, electrical charge, and composition into and out of the cell 2 types of transport 1. Passive – – Does not use energy Moves from a high concentration to a low concentration 2. Active – – Requires energy Moves from a low concentration to a high concentration Passive Transport- Terms • Equilibrium – Results when the concentration of a substance is the same through out a space • Concentration – The amount of a particular substance in a given volume • Concentration gradient – Occurs when one area has a higher concentration than another area does. Passive Transport-Simple Diffusion Diffusion • The movement of particles from regions of higher density to regions of lower density across the cell membrane. • The direction of movement depends on the concentration gradient and does not require energy. Passive Transport-Simple Diffusion Diffusion Facilitated Diffusion Passive Transport Facilitated Diffusion • Transport proteins – Helps ions and polar molecules diffuse through the membrane 2 types • Channel proteins or pores • Carrier proteins Passive Transport Facilitated Diffusion • Channel proteins or pores – Act as a tunnel through the membrane – Allow specific ions, sugars, and polar molecules to pass • Carrier – Transports substances that fit within their binding site – Results in changing the shape of the protein and the delivery of the substance to the other side of the cell Passive Transport Facilitated Diffusion Passive Transport: Osmosis Osmosis • the diffusion of water across a selectively permeable membrane • Allows cells to maintain balance as their environment changes. Passive Transport: Osmosis Passive Transport: Osmosis Water Channels • form of facilitated diffusion • Polar water molecules must rely on channel proteins in the cell membrane that only allow water molecules to pass through. Passive Transport: Osmosis Predicting Water Movement • Hypertonic – Water moves out • Hypotonic – Water moves in • Isotonic – Water diffuses in and out of the cell at an equal rate Effects of Osmosis • If left unchecked, the swelling caused by a hypotonic solution could cause a cell to burst. Ways to prevent the cell from bursting • rigid cell walls of plants and fungi prevent the cells from expanding too much. – many plants are healthiest in a hypotonic environment. • Some unicellular eukaryotes have contractile vacuoles – which collect excess water inside the cell and force the water out of the cell. • Animal cells have neither cell walls nor contractile vacuoles. – avoid swelling caused by osmosis by actively removing solutes from the cytoplasm. Active Transport Review • Requires energy • Moves against the concentration gradient – move from low concentration to high concentration Active Transport Pumps • Requires carrier proteins • Ex. sodium-potassium pump – sodium ions bind to the carrier protein – through the use of energy(ATP) changes shape releasing sodium to the outside of the membrane – while open to the outside, potassium ions bind to the carrier protein – when the pump returns to its original shape the potassium ions are released on the inside. – For every 3 sodium ions taken out there are 2 potassium ions taken in Active Transport Vesicles • Allows proteins, polysaccharides, and other substances that are too large to be transported by carrier proteins • Contain the same lipid bilayer as the membrane so vesicles can easily break off and fuse with the membrane 2 types • Exocytosis • Endocytosis Endocytosis • the movement of a large substance into a cell by means of a vesicle • cell membrane folds inward creating a pouch for the substance to enter • once in the pouch it pinches off and forms a vesicle • these vesicles can fuse with lysosomes and other organelles Active Transport Exocytosis • The movement of material out of the cell by the means of a vesicle • Reverse process of Endocytosis • Vesicles fuse with the cell membrane and releases its contents to the outside of the cell • Used to export proteins modified by the golgi apparatus Active Transport